Thermogravimetric and infrared spectroscopic studies of the spontaneous combustion characteristics of different pre-oxidized lignites

It is extremely important to prevent spontaneous combustion of coal in mines by studying the secondary oxidation of lignite at different pre-oxidation temperatures. The characteristic parameters of the spontaneous combustion of lignite were analyzed by simultaneous thermal analysis-Fourier transform infrared spectroscopy and in situ infrared spectroscopy experiments from the perspective of coal oxidizing, exothermicity and structural functional groups. The results show that the critical temperature and total heat absorption of pre-oxidized coal are lower than those of raw coal. For the coal a with pre-oxidation temperature of 120 °C, the critical temperature and total heat of the endothermic reaction were the lowest, which resulted in increased CO release and CO(2) gas production. In the low temperature stage, the pre-oxidation step weakens some functional groups in coal; however, the participation amount of –CH(3) structures increases. Kinetic analysis was performed on –OH and –CH(3) groups during the secondary oxidation of coal. After pre-oxidation, the activation energy of coal was lower than that of raw coal; it was the lowest when the pre-oxidation temperature was 120 °C. In summary, the risk of spontaneous combustion of pre-oxidized coal increases during secondary oxidation, and the risk is greatest when the pre-oxidation temperature climbs to 120 °C.